Prepare mix and bake according to package directions. Cool 10 minutes. Remove
from pan and cool completely. Place on a serving platter. Spread cake with the
1/3 cup ice cream topping. Chill until needed.

For mousse: In a small saucepan, melt semisweet chocolate over low heat; remove
from heat. Stir in powdered sugar, liqueur, and egg yolks. Cook and stir over
medium heat for 2 minutes or until mixture just coats a metal spoon. Remove from
heat; cool completely.

Beat the first 1/2 cup whipping cream with an electric mixer to soft peaks. Stir
HALF of the chocolate mixture into the whipped cream. Fold in remaining
chocolate. Cover; chill mixture just until it mounds. Spread onto cake within 1
inch of edge. Chill, covered, several hours.

To serve, drizzle cake with the 1 tablespoon topping. Beat the remaining
whipping cream to stiff peaks. Using a pastry bag fitted with a large star tip,
pipe whipped cream around cake edge.